I have tried following options.
BigDecimal expectedAmount = BigDecimal.valueOf(3000.00);
BigDecimal expectedAmount = BigDecimal.valueOf(3000);
BigDecimal expectedAmount = new BigDecimal(3000.00);
BigDecimal expectedAmount = new BigDecimal(3000);
You shall use the constructor accepting the String val as:
BigDecimal expectedAmount = new BigDecimal("3000.00");